Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of an embodiment of a display screen or portion thereof with a graphical user interface showing our new design.

The even length dashed broken lines are for environmental purposes only and form no part of the claimed design.

The outer perimeter shown in uneven length dot-dash broken lines represents a display screen or portion thereof and forms no part of the claimed design. The remaining uneven length dot-dash broken lines represent an unclaimed boundary line and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 